Heretofore, optical recording media such as MO, MD, CD-R, DVD-R, DVD-RW, and DVD+RW have been known as the one wherein so-called wobble which makes grooves being guide grooves to be a meandering state with a predetermined period. Such optical recording medium is arranged so as to utilize wobble for synchronization of rotation or to represent information by such wobble.
In this case, modes for utilization of wobble in these optical recording media may be classified into some types.
First, in case of MD and CD-R, wobble is modulated to represent information. Namely, wobble is FM-modulated to embed address information and the like in such MD or CD-R.
Such technique as described above has been clearly expressed, for example, in the accompanying drawings of Japanese Laid-Open No. 25460/1999.
Incidentally, a tendency of high density in magneto optical recording technology progresses in recent years. With such progress, a track pitch for an optical recording medium is narrowed increasingly. As a result, leakage of wobble signals from grooves constituting adjacent tracks becomes higher in so-called wobble signals, whereby an S/N ratio in the wobble signals reduces remarkably. In the case where FM modulation is applied to wobble signals, when leakage of the wobble signals from the above-mentioned adjacent grooves increases, it becomes difficult to discriminate a frequency of the leakage signal from that of information to be read, because the frequency of wobble is not constant. Thus, it becomes hard to read correctly information contained in the wobble.
In order to solve such problems as described above, there is a manner, which has been adopted, for example, in DVD-R and DVD-RW.
The manner has been disclosed in Japanese Patent Laid-Open No. 326138/1997 wherein pits are defined between wobbled grooves, and information is embedded in these pits, such pits being called by the name of land pre-pits (LPP).
In this manner, however, since pits are defined adjacent to grooves, data signals residing adjacent to the pits are influenced. Thus, there has been a problem of easy appearance of erroneous detection of data. Besides, the LPP themselves are affected also by data signals of adjacent grooves, so that there has been a problem of easy appearance of erroneous detection of LPPs.
On one hand, information is embedded in wobble itself in case of DVD+RW with a different form from that of the above-mentioned MD and CD-R. The manner for embedding information has been described in detail in written standards of EDMA wherein a wobble phase is deviated at a predetermined position by 180 degrees, and information is embedded by the use of the deviated wobble phase as a trigger.
In this manner, however, since the wobble phase is deviated too hastily, fabrication of a base plate for optical recording media is difficult so that scattering results occur easily in recorded signals. More specifically, when a block error rate (BLER: One (1) block is 1 ADIP Word) of the signals is measured by the use of a disk tester, it was confirmed that the block error rate was around 15% before recording data, while it was around 75% after recording data, and hence, the reading thereof was difficult.
According to such manner for representing information by wobble or a manner for affording information by the use of LPPs as mentioned above, format efficiency is very good so that it is suited for attaining high density as compared with an optical recording medium such as DVD-RAM wherein an address pit is formed on a head of data.
However, any of the above-mentioned conventional wobble formats involves both merits and demerits.